1. Field of the Invention
The present invention relates to a flexible tube for an endoscope, a material used for producing an outer cover of the flexible tube, and to a method of producing the flexible tube.
2. Description of the Prior Art
In an endoscopic examination, a flexible tube of an insertion section of an endoscope is to be inserted deep into the body cavity, for example, into the stomach, duodenum, small intestine or large intestine. For this reason, the flexible tube has to have sufficient flexibility (that is, the insertion section is required to have flexibility). This reduces the burden on patients. The flexible tube is roughly composed of a flexible elongated structural body (including an elongated coil) and an outer cover provided on the outer periphery of the structural body. The outer cover of the flexible tube serves to prevent body fluids and the like from entering the inside of the insertion section of the endoscope. In order to improve the ease of the inserting operation of the insertion section, the outer cover is also required to have sufficient flexibility. In the prior art, an elastic material such as polyurethane or the like has generally been used as a structural material for the outer cover of the flexible tube of the endoscope.
Now, because an endoscope is used repeatedly, it must be washed and sterilized after each use. However, such prior art materials have poor chemical resistance and heat resistance. Consequently, when such an endoscope is used repeatedly, the repeated sterilization of the endoscope using a peroxide disinfectant solution or high heat sterilizing treatment after each use will degrade the outer cover of the flexible tube. Further, as the outer cover of the flexible tube of the endoscope loses flexibility over time, it becomes difficult to smoothly insert the flexible tube into a body cavity. Furthermore, in the case where such degradation is severe, small cracks and the like will be created, and this can cause the outer cover of the flexible tube to partially peel off.
In view of the problems involved in the prior art described above, it is a main object of the present invention to provide an improved flexible tube for an endoscope having high chemical resistance and heat resistance as well as flexibility and a material used for producing the flexible tube.
Further, it is another object of the present invention to provide a method of producing such a flexible tube.
In order to achieve the above main objects, the present invention is directed to a flexible tube for an endoscope, comprising a flexible elongated structural body, and
an outer cover provided over the elongated structural body, the outer cover being made of a material which contains polyurethane elastomer and polyester elastomer, in which compounding ratio of the polyurethane elastomer and the polyester elastomer in the material is 0.03-0.3 parts by weight of the polyester elastomer per 1 part by weight of the polyurethane elastomer.
Thus formed flexible tube has excellent flexibility as well as excellent properties such as chemical resistance and heat resistance.
In this invention, it is preferred that the weight average molecular weight of the polyester elastomer lies within the range of 10,000-50,000.
Use of the material containing the polyester elastomer having the weight average molecular weight makes it possible that the polyurethane elastomer and the polyester elastomer are uniformly mixed in the material.
In the present invention, it is also preferred that the polyurethane elastomer and the polyester elastomer are contained in the material in a uniformly mixed state.
Another aspect of the present invention is directed to a material used for producing an outer cover of a flexible tube for an endoscope. The material comprising polyurethane elastomer and polyester elastomer, in which compounding ratio of the polyurethane elastomer and the polyester elastomer in the material is 0.03-0.3 parts by weight of the polyester elastomer per 1 part by weight of the polyurethane elastomer.
In this case, it is preferred that the weight average molecular weight of the polyester elastomer lies within the range of 10,000-50,000. Further, it is also preferred that the polyurethane elastomer and the polyester elastomer are contained in the material in a uniformly mixed state.
Yet another aspect of the present invention is directed to a method of producing a flexible tube for an endoscope. The method comprises the steps of: preparing a material which contains polyurethane elastomer and polyester elastomer, in which compounding ratio of the polyurethane elastomer and the polyester elastomer in the material is 0.03-0.3 parts by weight of the polyester elastomer per 1 part by weight of the polyurethane elastomer; heating the prepared material to such an extent that the material is melted or softened; and molding the material onto a flexible elongated structural body to form an outer cover of the flexible tube in the form of an elongated tubular form to obtain the flexible tube.
This method is capable of providing a flexible tube for an endoscope which has excellent flexibility as well as excellent properties such as chemical resistance and heat resistance.
In this method, it is preferred that before the molding step, the temperature of the material is held at 140-230xc2x0 C. This makes it possible to prevent the outer cover material from being hardened, deteriorated or degraded.
Further, it is also preferred that before the molding step, viscosity of the material lies within the range of 1.0xc3x97102-1.0xc3x97107 ps. Use of such a material makes it possible to produce the outer cover of the flexible tube having good weather resistance.
Furthermore, it is also preferred that the weight average molecular weight of the polyester elastomer lies within the range of 10,000-50,000. This makes it possible that the polyurethane elastomer and the polyester elastomer are uniformly mixed in the material.
In this method, it is also preferred that in the material preparing step, the material is stirred so that the polyurethane elastomer and the polyester elastomer are uniformly mixed to each other. For this purpose, it is preferred that in the material preparing step, the material is poured into a cylinder provided with a mixing screw, and then the material is stirred with the mixing screw under heated condition.
In this case, preferably, the mixing screw in the cylinder is rotated at a rotation speed of 2.0-30 rpm. This makes it possible to mix the components uniformly.
Further, in this method, it is also preferred that during the stirring process, rotation speed control of the mixing screw is carried out by switching a rotation speed mode between at least two modes having different rotation speeds. In this case, it is preferred that the rotation speed mode of the mixing screw is switched at least 2 times per one minute. Further, it is also preferred that the rotation speeds of the mixing screw in the rotation speed modes have a difference of at least 5.0 rpm. These methods also make it possible to mix the components more uniformly.
In this method, preferably, the molding step is carried out by means of extrusion molding.
These and other objects, structures and advantages of the present invention will be apparent more clearly from the following description of the invention based on the examples.